President Barack Obama on Wednesday named US ambassadors to Japan, India and Sri Lanka, amid heightened tension in Asia over North Korea's nuclear tests, unrest in Pakistan and ethnic tension in Sri Lanka.

Obama named longtime technology-focused lawyer John Roos as US ambassador to Japan, and named Democratic former congressman Timothy Roemer to be his envoy in India, the White House said.

Roemer served on the blue-ribbon commission investigating the September 11, 2001 terror attacks on the United States and on a key committee to prevent nuclear proliferation.

He represented a district from the midwestern state of Indiana from 1991 to 2003.

Roos is chief executive of the Wilson Sonsini Goodrich & Rosati law firm, and during his tenure "helped lead the firm during the various waves of innovation in Silicon Valley," according to a White House statement.

Obama also named Patricia Butenis, a career diplomat who has previously been posted in Baghdad, Pakistan and New Delhi, as ambassador to Sri Lanka and the Maldives.

The ambassadors will "strengthen our partnerships abroad at this critical time for our nation and the world," Obama said in the statement.

The ambassadorial positions still need confirmation by the US Senate.